Capacitive sensors can be used to detect position or proximity, and are often used in two-dimensional touchpads, touch displays, slide controls, and other types of input interfaces. These input interfaces are commonly utilized by mobile phones, computers, personal digital assistants, and other electronic devices. A device user operates such an electronic device by moving one or more fingers in proximity to or in contact with a sensing region of one or more capacitive sensors at the input interface.
Capacitive touch sensors operate by monitoring the change in capacitance above a parasitic capacitance background when a conductor such as the user finger comes in close proximity to or in contact with a sense electrode. The electrode may be exposed for direct contact or insulated with an insulating material over the sense electrode. In one typical configuration, if touched directly the capacitance added above parasitic capacitance is a body-PCB capacitance between the user finger (and/or body attached to the finger) and a printed circuit board (PCB) to which the sense electrode is attached via a sensing chip. The sense electrode is directly coupled to the sensing chip. Direct contact with the electrode offers the advantage of providing the largest signal, but can provide an electrostatic discharge (ESD) path into the electronics of the device in which the capacitive touch sensor is used.
If there is an insulator above the sense electrode which the user finger contacts, the increase in capacitance is due to the series combination of a body-electrode capacitance between the user finger and the sense electrode and the body-PCB capacitance. The body-PCB capacitance is usually very large so that the dominant increase in capacitance is due to the body-electrode capacitance.
Current capacitive sensors often have limitations with respect to accuracy, flexibility in placement, and use. As a result, improved apparatuses and methods for capacitive sensing are needed.